Method of using developer-finisher compositions for lithographic plates

ABSTRACT

A developing and finishing composition for lithographic printing plates containing: a. a mono-, di-, or tri-sodium, potassium or lithium phosphate; and b. benzyl alcohol, phenoxyethanol or phenoxypropanol; and c. polyvinyl pyrrolidone, dextrin, poly (methyl vinyl ether/maleic acid) or gum arabic; and d. citric acid or benzoic acid; and e. sodium or potassium octyl sulfate; and f. sodium, potassium or lithium benzoate; and g. sodium, potassium or ammonium citrate; and h. sodium, potassium or ammonium sorbate; and i. sufficient water to formulate an effective developer.

BACKGROUND OF THE INVENTION

The present invention relates to developer-finisher compositions forphotographic elements comprising photosensitive coatings on substrates,or more particularly to developer-finisher compositions for removing anddesensitizing the non-image areas of exposed, usually negative workinglithographic printing plates. Lithographic printing plates generally arecomposed of an aluminum containing substrate which may or may not havebeen treated with a variety processes recognized in the art processincluding anodization, graining and hydrophilization. The thuslyprepared substrate may then be applied with a photosensitive coatingcomprising a photosensitizer, binding resins, colorants, acidstabilizers, surfactants and other art recognized components. Commonphotosensitizers include diazo compounds, including polymeric diazoniumcondensates salts and photopolymerizable compositions. Sensitizers,binders and printing plates employing aromatic diazonium compounds aredescribed in U.S. Pat. Nos. 3,175,906; 3,046,118; 2,063,631; 2,667,415;3,867,147 and 3,679,419 which are incorporated herein by reference.

It is known in the art to prepare developing compositions forlithographic plates. Likewise desensitizing finishers are also known.Attempts have been made in the past to prepare single compositiondeveloper/finishers, however, these suffer from drawbacks such asincompatibility of the components. In general, one cannot simply mix adeveloper and a finisher to obtain a useful developer/finisher.Developer compositions remove the non-image portion of the plate afterit has been imagewise exposed. A finisher must function to desensitizethe non-image areas to assure that they will not accept greasy ink uponprinting. The finisher also prevents oxidation of the background areasof the plate during storage or while waiting for press mounting. Thefinisher must also be quickly removable from the plate so that it willnot cause production delays. Typically the finisher must be quicklyremovable by a water rinse or most preferably must be removable by thefountain solution used on the press. Quick rollup is then essential inorder to prevent paper waste and reduced production time. Thedeveloper-finisher should also bind removed non-image particles of thephotosensitive surface so they are not re-deposited back onto the plate.In the past, various methods of developing printing plates have beenemployed. Such methods include the use of compositions containingorganic solvents, surfactants, salts, acids and other art recognizedmaterials in solution. Typically prior art developing compositions aredescribed in U.S. Pat. Nos. 2,754,279; 4,381,340 and German OLS No.2,216,419. It is most desirable to have a developer composition which iscapable of completing development in a short period of time. Theoleophilic image areas of the printing plate should be ink receptive andwater repellant whereas the hydrophilic non-image areas should be waterreceptive and greasy ink repellant.

The proper selection of the solvent in a developer solution is veryimportant. If the selected solvent in a developer solution is a goodsolvent of the light sensitive composition itself, the solvent will notsatisfactorily distinguish between the exposed areas and the unexposedareas. As a result, a large portion of the image area coating isdissolved in the solvent or is severely swollen and removed. Suchprinting plates have no practical value. By the addition of a largeamount of water to reduce the concentration of the organic solvent inthe developer solution, image differentiation can be improved. However,during the development of a printing plate, particularly in negativeworking plates, nonimage areas comprising resin binders such as acetals,and particularly polyvinyl formal, solvate in the developer solution andseparate from the support and contract to spherical shapes in a highlytacky condition. Such solvated particles may otherwise deposit uponstill-solvent-wet image areas and adhere permanently even after drying.Not only are these "redeposited" areas visible to the naked eye on thedeveloped printing plate but are removed by tacky ink during printingwhich pulls away the true underimage, leaving skips which show asabsence of image on the printed sheet. A balance of developer propertiesis necessary where adequate speed of development is attained with aminimum of redeposited particles.

Efforts have been made to prepare developer/finishers which, as the namesuggests, develop and prepare a plate for the printing press or forstorage in a single operation. This objective has become particularlydesirable with the advent of processing machines. Examples of suchsolutions include U.S. Pat. No. 2,754,279 and German OffenlegungsschriftNo. 2,216,419. The latter two patents describe two-phasedeveloper/finishers.

In the use of both developers and developer/finishers in machines,problems arise in the etching and plating of the process as a result ofthe ingredients of the developer or developer/finisher.

It is an object of this invention to provide a developer anddeveloper/finisher for both machine and hand development of lithographicprinting plates having resin binders in their photosensitive coatings,which will enable the operator to prepare a plate free fromobjectionable redeposit. It is another object of this invention toprovide processing solutions which combine the above objects with goodhydrophilization of the nonimage areas and oleophilization of the imageareas.

These and other objects will become apparent in the detailed descriptionof the preferred embodiment.

SUMMARY OF THE INVENTION

The invention provides a developing, desensitizing and finishingcomposition for lithographic printing plates which comprises inadmixture:

a. from about 0.1% to about 10.0% by weight of the composition of one ormore compounds selected from the group consisting of mono-, di-, ortri-sodium, potassium or lithium phosphate; and

b. from about 0.1% to about 10.0% by weight of the composition of one ormore compounds selected from the group consisting of benzyl alcohol,phenoxyethanol and phenoxypropanol; and

c. from about 0.1% to about 10.0% by weight of the composition of one ormore resins selected from the group consisting of polyvinyl pyrrolidone,dextrin, poly (methyl vinyl ether/maleic acid) and gum arabic; and

d. from about 0.1% to about 10.0% by weight of the composition of one ormore acids selected from the group consisting of citric acid and benzoicacid; and

e.from about 0.5% to about 15.0% by weight of the composition of one ormore compounds selected from the group consisting of sodium or potassiumoctyl sulfate; and

f. from about 1.0% to about 15.0% by weight of the composition of one ormore compounds selected from the group consisting of sodium, potassiumand lithium benzoate; and

g. from about 0.2% to about 10.0% by weight of the composition of one ormore components selected from the group consisting of sodium, potassiumand ammonium citrate; and

h. from about 0.2% to about 15.0% by weight of the composition of one ormore components selected from the group consisting of sodium, potassiumand ammonium sorbate; and

i. sufficient water to formulate an effective developer.

The invention further provides a method for preparing a photographicelement which comprises imagewise exposing a photographic elementcomprising a light sensitive negative working or positive workingphotographic composition disposed on a substrate with sufficient actinicradiation to form a latent image and then simultaneously removing thenon-image areas of said exposed element and desensitizing the non-imageareas with a developer/finisher composition comprising the foregoingadmixture.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As the first step in the production of photographic elements such aslithographic printing plates, a sheet substrate such as aluminumcompositions suitable for the manufacture of lithographic printingplates such as, Alcoa 3003 and Alcoa 1100, which may or may not havebeen pretreated by standard graining and/or etching and/or anodizingtechniques as are well known in the art, and also may or may not havebeen treated with a composition, such as polyvinyl phosphonic acid,suitable for use as a hydrophilizing layer for lithographic plates iscoated with a light sensitive polymeric diazonium salt or photopolymercontaining composition. Such compositions may also contain bindingresins, such as polyvinyl formal resins, colorants, acid stabilizers,surfactants, exposure indicators or other art recognized ingredients.

The photosensitive sheet material is then exposed to a suitableradiation source through a mask or transparency, and the exposed sheetthen developed for removal of the non-image photosensitive materials.

The photosensitive coating mixture is usually prepared in a solventcomposition which is compatible with all the other compositioningredients. The light sensitive composition is then coated on thesubstrate and the solvent dried off.

Diazonium compounds most commonly employed in the preparation of lightsensitive compositions suitable for the present application may becharacterized by the generic structure A--N₂ ⁺ X⁻, wherein A is anaromatic or heterocyclic residue and X is the anion of an acid.

Specific examples of light sensitive negative working diazoniummaterials useful as aforementioned include higher molecular weightcompositions obtained, for example, by the condensation of certainaromatic diazonium salts in an acid condensation of certain compoundssuch as formaldehyde, as disclosed for example in U.S. Pat. Nos.2,063,631 and 2,667,415. A preferred class of diazonium compounds isdescribed in U.S. Pat. No. 3,849,392. All of the foregoing patents areincorporated herein by reference. A most preferred diazonium salt is thepolycondensation product of 3-methozy-4-diazo-diphenyl amine sulfate and4,4'-bis-methoxy methyl-diphenyl ether, precipitated as the mesitylenesulfonate, as taught in U.S. 3,849,392. Suitable photopolymerizablecompositions are also well known to the skilled artisan.

The present invention provides a method for developing and finishingsuch exposed photosensitive elements by contracting them, to remove thenon-image areas, using a developer/finisher which contains theaforementioned ingredients in an aqueous mixture. The mixture preferablyhas a pH which is in the range of from about 5.8 to about 7.8, morepreferably from about 6.0 to about 7.0 and most preferably from about6.3 to about 6.6.

The developer contains a sodium or potassium octyl sulfate surfactantcomponent which is present in a preferred range of from about 0.5% toabout 15.0% by weight of the developer. A more preferred range is fromabout 1.0% to about 10.0% and most preferably from about 4.0% to about7.0%.

The developer also contains from about 1.0% to about 15.0% by weight ofthe developer of one or more of sodium, lithium and potassium benzoate.A more preferred range is from about 2.5% to about 10.0% and mostpreferably from about 5.0% to about 7.5%.

The developer further contains from about 0.1% to about 10.0% by weightof the developer of one or more compounds selected from the groupconsisting of citric and benzoic acids. A more preferred range is fromabout 0.6% to about 5.0% and most preferably from about 0.6% to about1.5%. The developer also contains from about 0.1% to about 10.0% byweight of the developer of one or more compounds selected from the groupconsisting of mono-, di- or tri-sodium, potassium or lithium phosphate.A more preferred range is from about 0.5% to about 5.0% and mostpreferably from about 0.7% to about 1.5%.

The developer further contains from about 0.1% to about 10.0% by weightof the developer of one or more compounds selected from the groupconsisting of benzyl alcohol, phenoxyethanol, and phenoxypropanol. Amore preferred range is from about 0.5% to about 5.0% and mostpreferably from about 1.0% to about 2.5%.

The developer also contains from about 0.2% to about 10.0% by weight ofthe developer of one or more of sodium, potassium and ammonium citrate.A more preferred range is from about 0.5% to about 5.0% and mostpreferably from about 0.7% to about 2.0%

The developer further contains from about 0.2% to about 15.0% by weightof the developer of one or more compounds selected from the groupconsisting of sodium, potassium and ammonium sorbate. A more preferredrange is from about 0.5% to about 10.0% and most preferably from about1.0% to about 4.0%. The developer also contains from about 0.1% to about10.0% by weight of the developer of one or more resins selected from thegroup consisting of polyvinyl pyrrolidone, dextrin, poly (methyl vinylether/maleic acid) and gum arabic. A more preferred range is from about0.5% to about 5.0% and most preferably from about 1.0% to about 3.0%.The developer additionally optionally contains one or more componentsselected from the group consisting of sodium, potassium, magnesium andammonium sulfates and sulfites. When such are used, they are present inan amount of from about 0.01% to about 5.0% by weight of the developer.A more preferred range is from about 0.05% to about 1.5% and mostpreferably from about 0.1% to about 0.5%.

In the preferred embodiment, the developer of the present inventionpreferably contains optional minor amounts of a conventional anti-foamcomponent which aids in processing of the printing plate. Thiscomponent, when it is used is preferably present in an amount of fromabout 0.02% to about 0.05% by weight of the developer. One preferredanti-foam agent is Dow DB-31 which is a silicone type anti-foam. Thedeveloper then contains sufficient water to formulate an effectivedeveloper. The developer is capable of substantially completely removingthe non-image areas of a photographic element in about 2 minutes or lesswhile simultaneously removing substantially none of the image areas.Substantially none of the material comprising said non-image areas isre-deposited back onto said photographic element.

The following non-limiting examples serve to illustrate the invention.

EXAMPLE 1

An ENCO® A-30 negative working printing plate available commerciallyfrom Hoechst Celanese Corporation is imagewise exposed to actinicradiation in a manner well known to the skilled artisan. The thuslyexposed plate is then processed with the following developer/finishercomposition:

    ______________________________________                                        Ingredients        Weight Percent                                             ______________________________________                                        Soft water         79.506                                                     Citric acid        0.076                                                      Sodium citrate 2H.sub.2 O                                                                        0.923                                                      Lithium benzoate   6.944                                                      Potassium sorbate  2.311                                                      Sodium octyl sulfate                                                                             5.557                                                      Phenoxypropanol    1.853                                                      Monosodium phosphate                                                                             1.000                                                      Polyvinylpyrrolidone K--15                                                                       1.800                                                      Antifoam DB-31     0.030                                                      ______________________________________                                    

The plate develops cleanly in a customary developing machine withoutnoticeable background staining or re-deposit of removed plate coatings.

EXAMPLE 2

Example 1 is repeated with an Enco A-60 negative working printing plateavailable commercially from Hoechst Celanese Corporation. Similarresults are noted.

EXAMPLE 3

ENCO presensitized A-60 plates are imagewise exposed to 290 mJ/cm². Theexposed plates are hand developed by using the following developerfinisher:

    ______________________________________                                        Ingredients         Weight Percent                                            ______________________________________                                        Soft Water          79.506                                                    Citric Acid Anhydrous                                                                             0.076                                                     Sodium Citrate .2H.sub.2 O                                                                        0.923                                                     Lithium Benzoate    6.944                                                     Potassium Sorbate   2.311                                                     Sodium Octyl Sulfate                                                                              5.557                                                     Monosodium Phosphate                                                                              1.000                                                     Polyvinylpyrrolidone K--15                                                                        1.800                                                     Dowanol (R) PPH Glycol Ether                                                                      1.853                                                     Antifoam DB-1430    0.030                                                     ______________________________________                                    

DEVELOPMENT PROCEDURES

(i) An imagewise exposed ENCO A-60 plate is placed in the developingsink. The developer finisher (about 30 ml/sq ft) is poured and spreadover the plate surface. After 10 seconds of dwell time, the plate isdeveloped with cotton or Webril Appli-Pads until the background isclean. The plate is buffed dry without a water wash.

(ii) An imagewise exposed ENCO A-60 plate is placed on a stack ofNewspapers. The developer finisher is poured (30 ml/sq ft) and spreadover the plate surface. The plate is developed after a 10 second dwelltime with Webril Appli-Pads and buffed dry.

(iii) An imagewise exposed ENCO A-60 plate is placed on a chipboard. Theplate is developed with Webril Appli-Pads using 30 ml of developerfinisher per sq. ft of plate surface. The plate is then buffed dry.

The developed plates are put on a Heidelberg-Sork-3 press for a pressroll up test. The ink density is set at 1.2 for uncoated pater and 1.4for a coated paper. All the plates rolled up cleanly.

The devloped plates are placed in an environmental room at 26.7° C. and80% R.H. for 24 hours for a holdover test. The plates are put on theHeidelberg-Sork-3 press after a 24 hour holdover under humid conditions.An acceptable print quality is obtained.

    ______________________________________                                        Ingredients        Weight Percent                                             ______________________________________                                        Soft Water         83.950                                                     Sodium Octyl Sulfate                                                                             4.000                                                      Sodium Benzoate    7.500                                                      Monosodium Phosphate                                                                             0.500                                                      Trisodium Phosphate                                                                              0.500                                                      Polyvinylpyrrolidone K--15                                                                       2.500                                                      Benzyl Alcohol     1.000                                                      Antifoam DB-31     0.050                                                      ______________________________________                                    

    ______________________________________                                        Ingredients       Weight Percent                                              ______________________________________                                        Water             85.380                                                      Dextrin 955 SR    0.500                                                       Lithium Benzoate  6.000                                                       Potassium Sorbate 0.500                                                       Sodium Octyl Sulfate                                                                            4.500                                                       Sodium Citrate .2H.sub.2 O                                                                      0.500                                                       Citric Acid Anhydrous                                                                           0.090                                                       Carbowax 200      0.030                                                       Benzyl Alcohol    2.500                                                       ______________________________________                                    

    ______________________________________                                        Ingredients        Weight Percent                                             ______________________________________                                        Soft Water         83.300                                                     Lithium Benzoate   7.500                                                      Potassium sorbate  0.500                                                      Sodium Octyl Sulfate                                                                             3.000                                                      Monosodium Phosphate                                                                             1.000                                                      Polyvinylpyrrolidone K--15                                                                       1.500                                                      Benzyl Alcohol     2.000                                                      Carbowax 200       1.000                                                      Sodium Sulfite     0.200                                                      ______________________________________                                    

    ______________________________________                                        Ingredients         Weight Percent                                            ______________________________________                                        Water               76.306                                                    Citric Acid Anhydrous                                                                             0.076                                                     Sodium Citrate .2H.sub.2 O                                                                        0.923                                                     Lithium Benzoate    6.944                                                     Potassium Sorbate   2.311                                                     Sodium Octyl Sulfate                                                                              5.557                                                     Dowanol (R) PPH Glycol Ether                                                                      1.853                                                     Monosodium Phosphate                                                                              1.030                                                     Polyvinylpyrrolidone K--15                                                                        3.000                                                     Dowfax 2A1          2.000                                                     ______________________________________                                    

    ______________________________________                                        Ingredients       Weight Percent                                              ______________________________________                                        Water             82.880                                                      Dextrin 955 SR    2.000                                                       Lithium Benzoate  7.500                                                       Potassium Sorbate 2.500                                                       Sodium Octyl Sulfate                                                                            3.000                                                       Sodium Citrate Dihydrate                                                                        1.000                                                       Citric Acid Anhydrous                                                                           0.090                                                       Magnesium Sulfate .7H.sub.2 O                                                                   1.000                                                       Antifoam DB-31    0.030                                                       ______________________________________                                    

    ______________________________________                                        Ingredients          Weight Percent                                           ______________________________________                                        Water                82.380                                                   Gantrez S--95 (supplied by GAF)                                                                    2.500                                                    Lithium Benzoate     7.500                                                    Potassium Sorbate    2.500                                                    Sodium Octyl Sulfate 4.000                                                    Sodium Citrate Dihydrate                                                                           1.000                                                    Citric Acid Anhydrous                                                                              0.090                                                    Antofoam DB-31       0.030                                                    ______________________________________                                    

The developer finisher formulations of example 4 is evaluated by theprocedures of example 3 using ENCO A-60 plates and similar lithographicproperties are obtained as reported in example 3.

What is claimed is:
 1. A method of treating a photographic element whichcomprises imagewise exposing a positive working or negative workingphotographic element to sufficient actinic radiation to form a latentimage thereon, and then removing the non-image portions thereof andfinishing said element with:a developing and finishing compositioncomprising in admixture:a.from about 0.1% to about 10.0% by weight ofthe composition of one or more compounds selected from the groupconsisting of mono-, di-, or trisodium, potassium or lithium phosphate;and b. from about 0.1% to about 10.0% by weight of the composition ofone or more compounds selected from the group consisting of benzylalcohol, phenoxyethanol and phenoxypropanol; and c. from about 0.1% toabout 10.0% by weight of the composition of one or more resins selectedfrom the group consisting of polyvinyl pyrrolidone, dextrin, poly(methyl vinyl ether/maleic acid) and gum arabic; and d. from about 0.1%to about 10.0% by weight of the composition of one or more acidsselected from the group consisting of citric acid and benzoic acid; ande. from about 0.5% to about 15.0% by weight of the composition of one ormore compounds selected from the group consisting of sodium or potassiumoctyl sulfate; and f. from about 1.0% to about 15.0% by weight of thecomposition of one or more compounds selected from the group consistingof sodium, potassium and lithium benzoate; and g. from about 0.2% toabout 10.0% by weight of the composition of one or more componentsselected from the group consisting of sodium, potassium and ammoniumcitrate; and h. from about 0.2% to about 15.0% by weight of thecomposition of one or more components selected from the group consistingof sodium, potassium and ammonium sorbate; and i. sufficient water toformulate an effective developer.
 2. The method of claim 1 wherein saidcomposition further comprises from about 0.01% to about 5.0% by weightof the composition of one or more components selected from the groupconsisting of sodium, potassium, magnesium and ammonium sulfates andsulfites.
 3. The method of claim 1 wherein said composition furthercomprises an antifoam agent.
 4. The method of claim 1 wherein component(a) comprises monosodium phosphate, and component (b) comprises phenoxypropanol, and component (c) comprises polyvinyl pyrrolidone, andcomponent (d) comprises citric acid, and component (e) comprises sodiumoctyl sulfate, and component (f) comprises lithium benzoate, andcomponent (g) comprises sodium citrate and component (h) comprisespotassium sorbate.
 5. The method of claim 1 wherein component (a) ispresen in an amount of from about 0.7% to about 1.5%, and component (b)is present in an amount of from about 1.0% to about 2.5%, and component(c) is present in an amount of from about 1.0% to about 3.0% andcomponent (d) is present in an amount of from about 0.06% to about 1.5%,and component (e) is present in an amount of from about 4.0% to about7.0%, and component (f) is present in an amount of from about 5.0% toabout 7.5% and component (g) is present in an amount of from about 0.7%to about 2.0% and component (h) is present in an amount of from about1.0% to about 4.0%, wherein said amounts are based on the weight of thecomposition.
 6. The method of claim 4 wherein component (a) is presentin an amount of from about 0.7% to about 1.5%, and component (b) ispresent in an amount of from about 1.0% to about 2,5%, and component (c)is present in an amount of from about 1.0% to about 3.0% and component(d) is present in an amount of from about 0.06% to about 1.5%, andcomponent (e) is present in an amount of from about 4.0% to about 7.0%,and component (f) is present in an amount of from about 5.0% to about7.5% and component (g) is present in an amount of from about 0.7% toabout 2.0% and component (h) is present in an amount of from about 1.0%to about 4.0%, wherein said amounts are based on the weight of thecomposition.